1. Field of the Invention
The present invention relates to a method of examining the states of alignment of glass fibers of a pair of ribbon fiber cables by observing the images of the glass fibers obtained in two directions.
2. Description of the Related Art
When a pair of ribbon fiber cables are to be connected to each other, protecting covering on the portions of optical fibers of the fiber cables, which are adjacent to endfaces of the optical fibers to be connected, are removed so that glass portions i.e., glass fibers are exposed. These glass fibers are fitted into, V-shaped grooves on a pair of blocks, each having the same number of V-shaped grooves as that of the glass fibers in each of the fiber cables, in such a way that the glass fibers in one fiber cable fitted into the V-shaped grooves on one block are opposed to their paired glass fibers in the other fiber cable fitted into the V-shaped grooves on the other block. It is confirmed whether or not the glass fibers in one fiber cable are aligned with those in the other fiber cable, and they are then connected to each other.
The reason why the states of alignment of glass fibers of the fiber cables are examined is that the paired glass fibers opposed to each other are shifted from each other to their complete connection to be expected when the glass fibers are incompletely fitted into the V-shaped grooves, the glass fibers are incompletely exposed, as naked optical fibers, and something thus remains on their naked portions, or something like dust is left in the V-shaped grooves.
In the case of the single optical fiber, the conventional examination is carried out according to the method of observing an image obtained by viewing the state of alignment of glass fibers of fiber cables in one direction or images obtained by viewing it in two directions which are perpendicular to each other.
The conventional method of observing the image viewed in one direction can be applied to the ribbon fiber cables. However, it can be detected with considerable accuracy according to this method how the paired glass fibers are shifted from that axis along which they should be aligned in a direction perpendicular to the optical axis of illuminating light incident into them, but their shift from that axis in the same direction as the optical axis of illuminating light is detected with a large error. This makes the conventional method difficult to be employed.
On the other hand, the method of observing images viewed in two directions can be applied to the ribbon fiber cables with high detecting accuracy In the case of the ribbon fiber cables, however, illuminating light can be entered into the glass fibers in a direction normal to that plane on which the glass fibers are arranged side by side, but it cannot be entered into them in a direction perpendicular to the normal direction (or in that direction in which they are arranged side by side). It is therefore needed that the two directions in which illuminating light is entered into the glass fibers are determined to shift from the direction perpendicular to the normal direction as well as from the normal direction. Therefore, the following method can be used. Two light sources are used and they are entered into the glass fibers in these two directions which are shifted from the normal direction and also from the direction perpendicular to the normal direction. In this method, however, the space between two images obtained on the light receiving side by the pickup system (objective, television camera and the like) is large. In other words, the distance along which the system must be moved is relatively long. This causes the system to be bulky and complicated. In addition, the image processing time is long.